In recent years, it has been necessary to clarify and grasp environmental variation mechanisms, for example, a mechanism of heat transport in ocean, on a global scale in order to cope with environmental problems such as global warming. A high-performance marine monitoring system for that purpose is being pushed forward. In such a high-performance marine monitoring system, it is necessary to monitor vertical structures of, for example, physical parameters such as sea temperatures and chemical parameters such as salinity concentrations from a sea depth of about 2,000 m to a sea level, i.e., changes in various parameters in a direction of the depth of the sea. As an instrument for conducting such monitoring, is used an automatic control profiling float that can automatically control its own buoyancy according to a preset program, thereby permitting lifting movement, lowering movement and maintenance of a position in a vertical direction in the sea.
As a conventional profiling float, is known, for example, a float having a structure illustrated in FIG. 3.
In the example illustrated in FIG. 3, a profiling float 50 is equipped with, as a housing, a float chamber 51 made of, for example, a reinforced resin, which forms an airtight internal space, and is constructed by a buoyancy controlling mechanism 52 for controlling the degree of buoyancy acting on the whole of the profiling float 50, a measuring mechanism 53 for measuring various parameters in the sea, a data transmitting mechanism 54 for radio-transmitting the data obtained by the measuring mechanism 53, a control mechanism 55 for controlling these respective mechanisms and an electric power source device 56 for supplying a power source to these respective mechanisms.
The buoyancy controlling mechanism 52 is equipped with a fluid storage part 521 storing a fluid for control of buoyancy in the interior thereof, which is provided in the interior of the float chamber 51, and an elastically expandable and contractible bag-like bladder 522 provided in such a manner that an acting part thereof is located at the exterior of the float chamber 51. In the buoyancy controlling mechanism 52, the bladder 522 is connected to the fluid storage part 521 through a main passage 523A having a one-way transfer type pump device 524 for transferring the fluid for control of buoyancy, and a return passage leading to the fluid storage part 521 is formed by a branched passage 523B branched from the main passage 523A. This branched passage 523B is provided with a valve mechanism 525 controlling a flow rate of the fluid for control of buoyancy according to the degree of valve opening. Here, the one-way transfer type pump device means an irreversible pump device, which has a function of transferring a fluid only one direction from one to the other in the main passage 523A and cannot transfer the fluid in a reverse direction. The operation of the pump device is stopped, whereby the main passage 523A is in a closed state.
The measuring mechanism 53 is constructed by a sensor 531, for example, a conductivity-temperature-depth profiler (CTD Profiler), which is provided in an exposed state at the exterior of the float chamber 51, and a sensor circuit board 532 for controlling the sensor 531. The data transmitting mechanism 54 is constructed by a radio antenna 541, a part of which is provided in an exposed state at the exterior of the float chamber 51, and a transmission circuit board 542. The sensor circuit board 532 and the transmission circuit board 542 are electrically connected to the control mechanism 55.
A mass to volume ratio of the whole of the profiling float 50 is designed in such a manner that a value of effective buoyancy in the sea becomes negative, and the float sinks in a state that the fluid for control of buoyancy is not filled at all or scarcely filled in the interior of the bladder 522 and the volume thereof is minimum and in a minimum effective buoyancy state that the buoyancy acting on the profiling float 50 is minimum.
In the present description, the term “effective buoyancy” means a value obtained by [Buoyancy acting on the profiling float in water]—[The overall mass of the profiling float]. Accordingly, when the value of the effective buoyancy is negative, the profiling float moves downward in the sea. When the value of the effective buoyancy is positive, the profiling float moves upward in the sea. When the value of the effective buoyancy is zero, the profiling float stays in a vertical direction so as to keep a fixed depth in the sea.
The profiling float 50 having such construction as described above is generally thrown in the sea from, for example, a ship and subjected to observation. After thrown in the sea, regarding, for example, a series of operations that the float moves downward to a predetermined depth, drifts at this depth for a fixed period of time and then gradually moves upward to a sea level as a cycle, the profiling float 50 automatically executes this cycle in a preset period to measure various parameters in this process. For example, measured data obtained during the upward movement in the sea is radio-transmitted to a base station when the profiling float 50 surfaces on the sea level.
More specifically, the profiling float 50 thrown in the sea starts to move downward by closing the main passage 523A by the pump device 524 in a stopped state and closing the branched passage 523B by the valve mechanism 525 in a state that the fluid for control of buoyancy is not present at all or scarcely present in the interior of the bladder 522, thereby creating the above-described minimum effective buoyancy state.
When drive of the pump device 524 is started by a signal according to a proper program preset in the control mechanism 55 in this minimum effective buoyancy state, the fluid for control of buoyancy is supplied from the fluid storage part 521 to the bladder 522 through the main passage 523A, whereby the bladder 522 is elastically expanded according to the amount of the fluid for control of buoyancy supplied to gradually increase the effective buoyancy of the profiling float 50. As a result, the downward movement of the profiling float 50 is gradually slowed.
When the value of the effective buoyancy becomes zero, the drive of the pump device 524 is stopped, and the bladder 522 is kept in a state expanded according to the volume of the fluid for control of buoyancy, which is present in the interior of the bladder, whereby the profiling float 50 becomes a neutral buoyancy state that the effective buoyancy is zero. As a result, the profiling float 50 stays in a vertical direction so as to keep the depth in the sea.
When the fluid for control of buoyancy is continuously filled into the bladder 522 to further expand the bladder 522, the effective buoyancy is gradually increased, and the profiling float 50 starts to move upward in the sea when the value of the effective buoyancy becomes positive.
On the other hand, when the branched passage 523B is then opened by the valve mechanism 525 in the state that the drive of the pump device 524 has been stopped, the fluid for control of buoyancy existing in the bladder 522 is discharged into the fluid storage part 521 through the branched passage 523B by the elastic restoring force of the bladder 522 and external force applied to the bladder 522 from the outside, for example, seawater pressure, whereby the bladder 522 is contracted to reduce the volume thereof so as to lower the effective buoyancy. As a result, the profiling float 50 moves downward again in the sea when the value of the effective buoyancy becomes negative.
In other words, according to such a profiling float 50 as described above, the volume of the fluid for control of buoyancy filled into the interior of the bladder 522 is controlled, whereby the volume of the bladder 522 is controlled, so that changes in the effective buoyancy attending on the changes in the volume of the bladder 522 permit the profiling float to move upward, move downward and stay in the vertical direction in the sea.
In such a profiling float for observation as described above, it is necessary to minutely control the effective buoyancy of the profiling float for controlling a predetermined moving speed and a stay depth with high accuracy. Such control of the effective buoyancy is achieved by minutely controlling the volume of bladder, i.e., the volume of the fluid for control of buoyancy existing in the interior of the bladder, by the pump device 524 and the valve mechanism 525.
In the profiling float 50 having such construction as described above, the same degree of pressure as the seawater pressure applied to the bladder 522 is applied to the valve mechanism 525 through the fluid for control of buoyancy. However, the valve mechanism 525 is difficult from the mechanism thereof to strictly control the degree of opening of the valve under pressure. After all, it is difficult to minutely control the flow rate of the fluid for control of buoyancy discharged from the bladder 522, so that it is difficult to minutely control the amount of the fluid for control of buoyancy within the bladder 522. Accordingly, the profiling float involves a problem that the predetermined effective buoyancy value can be realized with high accuracy, and after all, it is actually very difficult to realize the predetermined moving speed of the profiling float 50 and the operation in the sea such as the staying in the vertical direction at the predetermined depth with high accuracy. In addition, the float involves a problem that since the pressure applied to the valve mechanism 525 is considerably high when the profiling float 50 is located at a deep depth in particular, the above-described problem becomes more marked.
In addition, the valve mechanism 525 involves a problem that the amount of the fluid for control of buoyancy passing through the valve mechanism 525 varies according to, for example, the pressure applied to the fluid for control of buoyancy even when the degree of opening of the valve is kept constant, so that the amount is not fixedly stabilized, and after all, it is difficult to accurately control the flow rate of the fluid for control of buoyancy.
Patent Art. 1: Japanese Patent Application-Laid-Open No. 2002-145177.